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Friday, March 19, 2010

Suspension setup

Car-related forums are littered with the same n00b question: What coilover should I get for my Blah-Blah-Blah car. Most of the time the poster is only concerned about lowering the car for looks and will never use any of the adjustments available with a coil-over suspension. If, however, you want to really use these adjustments, you've got to learn the fundamentals. You need to know how camber and caster interact as the car turns in. You need to know how ride height changes at one end of the chassis effects mid-corner balance. There are a number of books on chassis engineering and a number of great web-sites that cover everything you would need.Now you may know what each adjustment does, but you won't make proper use of your new knowledge until you learn to think like a test driver and a race engineer. You have to measure and record everything. You have to take copious notes and be organized, methodical and work to a plan. Every session has to be on the clock and all performance measured.Now are you can start to use suspension adjustments to "tune" the suspension and gain real performance results.

What I'm going to describe here is setting up a Ground Control suspension system with Advanced Design Double Adjustable (D/A) shocks. With this system I can adjust nearly everything front and rear: Caster, Camber, Ride-height and Toe.The shocks are called double adjustable because it provides for two separate resistance adjustments, one changes the shocks resistance to being compressed (Bump) and the other changes the shocks resistance to being extended (Rebound). Single Adjustable shock have a single adjustment the usually only changes Bump resistance.The ability to adjust Bump and Rebound separately is tool that is use to change chassis balance on corner-entry and on corner-exit. Springs and Bars are use to change steady state chassis balance and shocks are used to adjust dynamic chassis balance.

I'm using Bump and Rebound because the first letter corresponds the the color of the knob used to make that adjustment. Red is for Rebound and blue is for Bump. These knobs stick out of the top of the shock so all adjustments are made under the hood or in the trunk and not from the bottom of the car.

The Advanced Design shocks described here have very different methods for setting Bump and Rebound. The blue knob (Bump adjustment) has three positions and a small detent to indicate the correct position. The red Rebound knob has three full turns of adjustment limited by small stops at full stiff and full soft. Clockwise is always stiffer on these shocks.

Baselining:

This is where you develop a repeatable basic setup for the car. All subsequent adjustments are made from from the baseline. My initial baseline came from Ground-Control and is basically an alignment/ride height guide. I have that on the car now. Once the ride heights are determined all the other adjustments won't alter the corner weights so I want to get it set before I corner-weight the car. I want to understand the performance envelope of the shocks so I plan to do a number of short sessions while testing full-soft through full stiff for both Bump and Rebound.